A recent study of the occurrence of otitis media (OM) in 2570 infants showed that one-third of visits to pediatricians "for illness of any kind resulted in the diagnosis of disease of the middle ear." The authors concluded that "any intervention to decrease the incidence of acute OM or to hasten the resolution of middle-ear effusions would substantially reduce the costs of providing care to children." Later studies of the same children demonstrated an association of chronic OM with lower scores in tests of speech and language development. This association was strongest in children who had persistent middle ear effusion in the first 6 months of life. Our studies of the occurrence of OM in infancy have provided criteria for early detection of infants who are at extraordinarily high risk for recurrent middle-ear infection and persistent middle ear effusion. Development of preventive measures for use in these infants is a long-range objective of our research. Bacterial Polysaccharide Immune Globulin (BPIG) is a special immune globulin (gamma-globulin) which is being developed by the Massachusetts Public Health Biologic Laboratories and American Red Cross for prevention of infections caused by the bacterial species which most frequently cause OM. This study is to be a controlled trial of BPIG for prevention of acute OM in young children. High-risk children in the first year of life for whom parental consent is obtained will be given BPIG or placebo injections at entry into the study and one month later. During the 4-month study period we will perform tympanocentesis (collection of fluid from the middle ear) to define the bacteria which cause episodes of acute OM. Studies will also be performed to establish the immunologic effects of BPIG therapy in these children. The major result to be sought will be detection of a clinically useful and statistically significant reduction in attacks of OM caused by bacteria against which the globulin donors have been immunized. This study represents a unique approach to prevention of recurrent OM. Based on the established safety of immune globulins which are in general use for preventing infections, BPIG may have significant advantages over the widely accepted use of drugs and surgery for this disease. The study will also provide novel and important information about the role of immunity in OM.